Atrial Natriuretic Factor: Production & Role

Atrial natriuretic factor (ANF) is also known as the hormone of the heart. This is a hormone-like substance that is present in the two atrial walls of the heart specifically in the right atria. The ANF is a hormone that is based on protein, produced and released by the cardiac muscle cells. 

• ANF is a vasodilator involved in the homeostatic management of body fluids, fats, potassium, and sodium in adipose tissue, a central metabolic organ in the body that supports energy homeostasis.
• The atrial natriuretic factor is a 28-amino acid polypeptide hormone made and released by the walls of the heart’s atria when stretched in an abnormal way.
• ANF changes the way the kidneys work to make more sodium and water leave the body.
• There are various types of Atrial Natriuretic factors such as urodilatin, B-type natriuretic peptide (BNP), C-type natriuretic peptide (CNP), and Dendroaspis natriuretic peptide (DNP). These are related paracrine hormones.
• The first member of the Natriuretic Peptide is the AtrB-type Natriuretic peptide is secreted from ventricles.
• Atrial natriuretic factor is also called Atrial natriuretic peptide (ANP), Atrial natriuretic hormone, or Atriopeptin (ANH).

Read More: Pancreas

Key Terms: ANF, Chromosome, Heart, Vasodilator, Atrial Natriuretic Factor, Polypeptide Hormone, ANH

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Atrial Natriuretic Factor

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Atrial natriuretic factor (ANF) is known as the heart hormone. It is a protein-based hormone that heart muscle cells secrete and release. 

• Through cardiac muscle cells, hormones are generated and delivered into the atrium to counteract high blood pressure. 
• Atriopeptin is another name for Atrial Natriuretic Factor.
• ANF is a crucial vasodilator involved in the homeostatic regulation of bodily fluids, salt, potassium, and adipose tissue fats.
• The main function performed by the Atrial Natriuretic Factor is that it controls and reduces the expanded extracellular fluid (ECF) volume in the body by increasing the renal sodium excretion. 
• It is synthesized and produced by the cells of cardiac muscles in the atria walls of the human heart. 
• The Volume receptors contained by the cardiac muscle cells help in responding to increased stretching of the atrial wall which happens due to increased arterial blood volume.
• Atrial Natriuretic factor acts as an essential Vasodilator involved in the regulation of body fluids and fats as well as sodium and potassium.
• It inhibits the renin from JGA (Juxtaglomerular apparatus)
• One of the most essential roles of the Atrial Natriuretic factor is it regulates kidney function by resisting the regulation of the Renin-Angiotensinogen Aldosterone system.

Cardiac Distension

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Production of ANF

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The Atrial Natriuretic Factor (ANF) is synthesized as the inactive peptide hormones which are encoded by the human natriuretic peptide A (NPPA), which is a gene located on the short arm of chromosome.

The ANF is produced and released in response to:

• Mental Stress or injury
• Due to increased sodium concentration that is Hypernatremia
• It is produced, stored, and released by cardiac myocytes of the atria of the heart.
• Due to the stretching of the atrial wall induced by the exercise, hypervolemia, and caloric restriction, the ANF is released.
• Due to Increased sympathetic stimulation of adrenoceptors
• Due to Acute Kidney Injury (AKI)

ANP Controlling Abnormally High Blood Volume

The ANP is released for the most potent stimulus of an atrial stretch which is due to the abnormally high circulating blood volume. To normalize and restabilize this condition, ANF leads to the enhanced elimination of water and sodium in the urine. Thus,

1. When the glomerulus' afferent arteriole is widened, filtration and blood flow increase. Water and urine volume increase as reabsorption slows and glomerular filtration increases. It's diuresis.
2. ANP reduces salt in the inner medullary collecting duct and other nephron segments. Natriuresis is the excretion of filtrate sodium in urine if sodium reabsorption is blocked.
3. Also, the ANP inhibits Na⁺/Cl^- reabsorption in the distal tubule and Na⁺/H⁺ exchange in the proximal tubule, both of which enhance the excretion of sodium.

The atrial natriuretic factor can lead to about a 3-10 times increase in renal or kidney excretion of sodium when it is completely released into the circulating blood. 

As a result of the loss of sodium, there is a slight decrease in the volume of the extracellular fluid and blood. However, it is believed that the ANF plays a significant role in stabilizing and regulating the blood volume in the body.

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Physiological Effects of Atrial natriuretic factor

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Atrial natriuretic factor acts on various organs as well as on the functions of the human body and it is mainly involved in the following physiological effects.

• It acts as an anti-hypertensive hormone.
• To reduce the blood pressure, it dilates the blood vessels.
• The atrial natriuretic factor helps in the reduction of reabsorption of sodium by acting on several nephron segments and other inner medullary collecting ducts.
• ANF has also been involved in the increase of the flow of renal blood along with an increase in the rate of glomerular filtration through the Vasodilation process or we can simply say the widening of blood vessels.
• Atrial Natriuretic factors decrease the blood pressure throughout the body.

ANP production

• Atrial Natriuretic factor is secreted which causes dilation of the blood vessels and therefore it decreases the blood pressure in the circulatory circulation.
• As the excretion of sodium increases  ANP reduces ECF (Extracellular fluid) volume. 
• When there is a loss of sodium, there is a slight decrease in the volume of the extracellular fluid and blood. It is believed that the ANF plays a significant role in stabilizing and regulating the blood volume in the body.
• So this follows with certain side effects such as a decrease in the extracellular fluid it improves cardiac ejection fraction, and lowers blood pressure.
• ANF blocks renal vasoconstriction and inhibits renin secretion.
• For the treatment of Individuals suffering from Hypertension.
• In vitro, it relaxes Angiotensin II.

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Therapeutic Perspectives of ANF

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Atrial natriuretic factor decreases systemic blood pressure and increases the quantity of sodium expelled. Therefore, ANF is a potential candidate for usage as a drug in the treatment of hypertension and congestive heart failure. 

• ANF can only be administered intravenously and its half-life is only three to four minutes. 
• There are currently no drugs that can be utilised to stimulate ANF secretion. 
• It has been claimed that decreasing the rate at which endogenous ANF is catabolized may result in an increase in plasma ANF levels.

Read More: Systolic and Diastolic Blood Pressure

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Role of ANF in Kidney Function

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ANF is the hormone for the heart. This molecule is found in the right atrium. It acts like a hormone. The protein-based ANF hormone is sent out by the heart muscle cells.

• Increasing arterial pressure strains the atrial wall. ANF is a 28-amino acid polypeptide hormone secreted by squeezed atria. 
• ANF increases Glomerular filtration and renal salt excretion. It prevents renal blood channels from narrowing and renin production. 
• ANF relaxes arteries and transfers cardiac fluid.
• ANF stops the adrenal glands from making aldosterone. 
• ANF is a reaction to both short-term and long-term volume overload. 
• The ability of ANF to move fluid from the vascular to the interstitial compartments acts as a buffer, keeping the volume of plasma from rising too much when extracellular fluid levels rise. 
• Through natriuresis, ANF changes GFR and salt loss.

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Atrial Natriuretic Factor Blood Pressure

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In intact animals, atrial natriuretic factor (ANF) lowers blood pressure and acts as a vasodilator. ANF relaxes angiotensin II-contracted arteries in a lab setting.

Renin-dependent models of renovascular hypertension appear to be more responsive to the blood pressure-lowering effects of ANF in vivo as compared to other experimental hypertensive models.

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Things to Remember

• ANF is administered intravenously with a half-life is only three to four minutes. 
• The presence of ANP was the first NP to be identified in heart tissue.
• Atrial natriuretic factor (ANF) is a peptide that was found in the secretory granules of atrial muscle cells.
• Atrial tissues contain similar-structured peptides. These peptides all share the same precursor consisting of 152 amino acids.

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